Re: set-frame-parameter a child-frame's 'parent-frame error on macOS ?

[martin rudalics]

> Might software rendering work, then? The way to use it depends on the video 
player, etc.

I'm afraid that video formats are not suitable to visualize ephemeral
effects that show only for one or a few keyframes.

> Feng Shu has changed his code since to call set-frame-position much
> less often, and it seems to work correctly *without* Robert's
> patch.

I recall having had a discussion with someone who insisted on using
`set-frame-position' immediately after making a new frame with the
argument that it always used to work.  In my experience this may
confuse the hell out of the window manager and even if it does work
for years it may cease to do so after an update of your system.  As a
rule, I try to position a frame initially only via parameters passed
to `make-frame'.

> Quite weird.

Basically, positioning and sizing child frames work like positioning
and sizing the scroll bar or tool bar windows.  If scaling is needed
for the latter, it is probably also needed for child frames.

martin